1. Field of the Invention
The present invention relates to a valve timing control system and method for an internal combustion engine, which can change opening and closing timings of either an inlet valve or an exhaust valve of the internal combustion engine in accordance with an engine operating condition.
2. Related Art
A typical conventional valve timing control system for an internal combustion engine is disclosed in Japanese Patent Application Laid-Open No. 64-80733. This system includes an electronic throttle system for controlling the opening angle of a throttle valve by driving an electric motor in accordance with accelerator position or the like, and a valve timing control mechanism (valve operation changing mechanism) for changing the opening and closing timings of the inlet valves of the internal combustion engine in accordance with an operating condition. A shock effect is cancelled, which is otherwise caused by the torque difference occurring when a cam in the valve timing control mechanism is changed over by changing the relation between the position of the accelerator pedal and the opening angle of the throttle valve.